Wireless non-contact communication systems have previously been proposed.
One such system is generally known as a near field RFID (Radio Frequency Identification) system, and employs a near field RFID tag and a near field RFID reader for reading information stored on the tag by means of magnetic field (H-field) inductive coupling between the reader and the tag. Near field RFID tags are referred to below as tags. Near field RFID readers are referred to below as readers. Readers and tags are together referred to below as RFID devices.
Such tags typically include an antenna, a controller and a memory (which may be part of the controller) in which information (for example information about the article to which the tag has been attached, control data or program data) is stored or may be stored.
For so-called passive RFID tags, a compatible reader uses a radio frequency (RF) signal (for example a signal at 13.56 MHz) to generate a magnetic field and when the antenna of the tag is in close proximity to the reader the magnetic field (H-field) generated by the reader is inductively coupled from the reader to the tag resulting in derivation and supply of power to the controller. Supply of power enables operation of the tag, for example enabling the tag controller to operate and access the memory and transmit information from the memory via the tag antenna to the reader. Transmission of information from the memory will be through modulation of the supplied magnetic field (H field). In this context a compatible reader is a reader operating at the same radio frequency as the tag and in accordance with the same communication protocols.
RFID readers typically include an antenna, controller, memory (which may form part of the controller), signal generator, modulator (for modulating a generated RF signal with data from either the controller and/or memory) and demodulator (for demodulating a modulated RF signal received from for example an RFID tag.
Illustrative RFID devices are described in various international standards, for example ISO/IEC 14443 and IASO/IEC 15693.
In addition to RFID devices of the types described above, it has also previously been proposed to provide so-called Near Field Communications (NFC) devices.
NFC devices, often referred to as NFC communicators (which two terms may be used interchangeably), are radio frequency non-contact communications devices that can communicate wirelessly with other NFC devices and/or RFID devices over relatively short ranges (for example a range in the order of several centimeters up to a maximum range of in the order of a meter or so). Communication is via inductive coupling of a magnetic field (H field) between the NFC communicator and a second NFC communicator or RFID device.
Illustrative NFC devices and systems are described in ISO 18092 and ISO 21481, and the operation of such NFC devices depends on whether they are operating as an “initiator” or a “target”, and whether they are operating in a “passive communications mode” or an “active communications mode”. As will be apparent from the following, the terms “passive” and “active” in the context of NFC devices do not have the same meaning as “passive” and “active” when used in the context of traditional RFID devices.
An initiator NFC device will generate an RF field and start communication. A target device will respond to receipt of an RF field from an Initiator NFC device. Response will be through modulation of the supplied RF field or through generation of a new RF signal and modulation of that RF signal.
In a “passive communications mode” the Initiator NFC Device will generate an RF field and the Target NFC device will respond to an Initiator command by modulation of the received RF signal, usually by load modulation. In an “active communications mode both the Initiator FC device and the Target NFC Device use their own RF field to enable communication.
It will be apparent from the foregoing that a first NFC device can operate in a passive mode (in a manner akin to a conventional RFID tag) and use an RF field generated by a conventional RFID reader or a second NFC device to respond to that reader or second NFC device. Alternatively, the first NFC device can operate in an active mode to generate an RF field for interrogating a conventional RFID tag or for communication with a second NFC device that may be operating in a passive or an active mode (i.e. either by using the RF field generated by the first device to communicate with the first device or by generating its own RF field for communication with the first device).
This allows such NFC devices to communicate with other NFC devices, to communicate with RFID tags and to be ‘read’ by RFID readers.
NFC devices may be in stand-alone form (either hand-held or free-standing) or comprised within other apparatus (either in stand-alone form or by being integrated within the other apparatus), for example a mobile transceiver (such as a mobile telephone), a personal digital assistant (PDA), an item of computer equipment such as a personal or portable computer, or a vending machine. NFC devices can be implemented by means of a single integrated circuit (a so-called one-chip solution or system on chip) or alternatively by means of separate functional component parts or separate integrated circuits. Such apparatus is referred to variously herein as NFC communications enabled devices, NFC Communicators, host apparatus and host devices.
All NFC devices are designed to communicate within a particular range or field of operation, for example a few centimeters. It is important to ensure both consistency of operation and optimal range for any given NFC device. The range of operation can be affected by a variety of environmental factors, for example the presence of magnetic materials in close proximity to the NFC device, the host apparatus within which the NFC device is comprised (for example the position of the battery within the host apparatus), the application for which the NFC device is intended (for example whether the environment is a controlled environment or variable), and human contact with the device. To reduce any effect on range NFC devices are designed to be tuned, for example by selecting appropriate external component values (for example by addition of capacitors), to compensate for impedance effects in a non-tuned antenna arrangement. This necessity to tune NFC devices is exacerbated where the NFC device is intended for use within a series of host apparatus or variants of host apparatus. For example where the NFC device has been designed for use in a given manufacturer's range of mobile phones (cell phones), and it is desired to avoid having to use different NFC devices for each mobile phone in the range of mobile phones offered by that manufacturer, the NFC device will need to be tuned specifically to each mobile phone in the range. This tuning is expensive and drives down the number of devices produced per unit time, drives up the unit cost of each device, and ultimately adversely affects the profitability of the manufacturing enterprise. Furthermore, even once tuned for the host apparatus, the NFC device capacitance is fixed and therefore the NFC device operation may still be affected by changes in the external environment.
This tuning issue has previously been addressed either by modifying the NFC device to include internal capacitors (i.e. capacitors within the NFC circuitry) in series or parallel with the antenna of the NFC device, or by modifying the device to include appropriate contacts for connection to external capacitors (i.e. capacitors external to the NFC circuitry).
In both cases, RFID devices have tended to incorporate conventional flat-plate-construction capacitors (such as poly-poly or metal-insulator-metal or vari-cap diodes capacitors and other well known equivalents) formed during integrated circuit manufacture. These capacitors have tended to be formed from electrodes on different layers or planes and as a result have a fixed breakdown voltage determined by the extent of gap between the different layers or planes. Thus where higher breakdown voltages are required (for example during power derivation or in NFC devices) further capacitors are required (either internal or external) which increases silicon area, and therefore cost, and reduces design flexibility.
In addition existing RFID devices require ‘tuning’ i.e. selection of appropriate capacitance values following manufacture and/or integration into a host apparatus. Such tuning adds to the overall manufacturing process and hence affects the profitability of the process for the manufacturer. The tuning process is also time consuming and has to be done for each product and each new product variant.
It would therefore be highly advantageous if a tuneable NFC device could be devised that addressed some or all of these problems and thereby provided a manufacturer with the ability to increase the platform insensitivity of such devices, for example by facilitating adaptation of devices for different customer applications. One object of the present invention is to provide such a device. It would also be desirable if a device could be devised that enabled compensation of external factors that might otherwise influence proper operation of the device.
Furthermore it would also be desirable if the circuitry employed for such a device were to address the problems that have hitherto affected internal and external solutions, and another aim of the present invention is to provide such a circuit arrangement.